Azimuth measurement technology in downhole is mostly categorized into measurements with magnetometers and measurements with gyro sensors. The former uses triad magnetometers to measure earth magnet field. However, the magnetometers can be used only in the place without any magnetic influence by magnetic materials like a casing. The latter uses gyro sensors to measure earth rate vector direction for azimuth determination. The gyro measurements are hardly influenced by magnetic field. Therefore, the gyro sensor can be used near or in such a casing of magnetic materials.
Some gyro sensors may show a large and instable bias, comparing with the earth rate (15°/hour). Also, some gyro sensors have low signal-to-noise ratio. Further, scale factor of some gyro sensors may be temperature sensitive. Measurement error due to such large and instable bias, low signal-to-noise ratio and temperature-sensitive scale factor are significant for MEMS (Micro-Electro Mechanical Systems) gyro sensors in particular, while the MEMS gyro sensors have preferable features for downhole use; cheap, light weight, shock reliable and high temperature resistant. Typically, total measurement error is required to be reduced in the range of less than 1°/hour to determine azimuth with sufficient accuracy like ±a few degrees. Therefore, there is a need for improved methods and systems that are capable of measuring azimuth accurately if such gyro sensors are used, for example, in oilfield and any other harsh environment.